Add chibicc

This program popped up on Hacker News recently. It's the only modern
compiler I've ever seen that doesn't have dependencies and is easily
modified. So I added all of the missing GNU extensions I like to use
which means it might be possible soon to build on non-Linux and have
third party not vendor gcc binaries.

third_party/chibicc/test/string_test.c

@@ -0,0 +1,105 @@
+#include "third_party/chibicc/test/test.h"
+
+int main() {
+  ASSERT(0, ""[0]);
+  ASSERT(1, sizeof(""));
+
+  ASSERT(97, "abc"[0]);
+  ASSERT(98, "abc"[1]);
+  ASSERT(99, "abc"[2]);
+  ASSERT(0, "abc"[3]);
+  ASSERT(4, sizeof("abc"));
+
+  ASSERT(7, "\a"[0]);
+  ASSERT(8, "\b"[0]);
+  ASSERT(9, "\t"[0]);
+  ASSERT(10, "\n"[0]);
+  ASSERT(11, "\v"[0]);
+  ASSERT(12, "\f"[0]);
+  ASSERT(13, "\r"[0]);
+  ASSERT(27, "\e"[0]);
+
+  ASSERT(106, "\j"[0]);
+  ASSERT(107, "\k"[0]);
+  ASSERT(108, "\l"[0]);
+
+  ASSERT(7, "\ax\ny"[0]);
+  ASSERT(120, "\ax\ny"[1]);
+  ASSERT(10, "\ax\ny"[2]);
+  ASSERT(121, "\ax\ny"[3]);
+
+  ASSERT(0, "\0"[0]);
+  ASSERT(16, "\20"[0]);
+  ASSERT(65, "\101"[0]);
+  ASSERT(104, "\1500"[0]);
+  ASSERT(0, "\x00"[0]);
+  ASSERT(119, "\x77"[0]);
+
+  ASSERT(7, sizeof("abc"
+                   "def"));
+  ASSERT(9, sizeof("abc"
+                   "d"
+                   "efgh"));
+  ASSERT(0, strcmp("abc"
+                   "d"
+                   "\nefgh",
+                   "abcd\nefgh"));
+  ASSERT(0, !strcmp("abc"
+                    "d",
+                    "abcd\nefgh"));
+  ASSERT(0, strcmp("\x9"
+                   "0",
+                   "\t0"));
+
+  ASSERT(16, sizeof(L"abc"
+                    ""));
+
+  ASSERT(28, sizeof(L"abc"
+                    "def"));
+  ASSERT(28, sizeof(L"abc"
+                    L"def"));
+  ASSERT(14, sizeof(u"abc"
+                    "def"));
+  ASSERT(14, sizeof(u"abc"
+                    u"def"));
+
+  ASSERT(L'a', (L"abc"
+                "def")[0]);
+  ASSERT(L'd', (L"abc"
+                "def")[3]);
+  ASSERT(L'\0', (L"abc"
+                 "def")[6]);
+
+  ASSERT(u'a', (u"abc"
+                "def")[0]);
+  ASSERT(u'd', (u"abc"
+                "def")[3]);
+  ASSERT(u'\0', (u"abc"
+                 "def")[6]);
+
+  ASSERT(L'あ', ("あ"
+                 L"")[0]);
+  ASSERT(0343, ("\343\201\202"
+                L"")[0]);
+  ASSERT(0201, ("\343\201\202"
+                L"")[1]);
+  ASSERT(0202, ("\343\201\202"
+                L"")[2]);
+  ASSERT(0, ("\343\201\202"
+             L"")[3]);
+
+  ASSERT(L'a', ("a"
+                "b"
+                L"c")[0]);
+  ASSERT(L'b', ("a"
+                "b"
+                L"c")[1]);
+  ASSERT(L'c', ("a"
+                "b"
+                L"c")[2]);
+  ASSERT(0, ("a"
+             "b"
+             L"c")[3]);
+
+  return 0;
+}